The brown marmorated stink bug is an invasive pest now established across much of Washington state, found in 29 of the state’s 39 counties as of 2020. Native to East Asia, it likely arrived in the United States in a shipping crate in the late 1990s and has since spread into homes, gardens, and orchards throughout the Pacific Northwest. If you’re dealing with these shield-shaped insects in or around your home, here’s what you need to know.
Why Washington Has a Stink Bug Problem
The brown marmorated stink bug (Halyomorpha halys) feeds on more than 170 plant species, including tree fruit, grapes, berries, vegetables, corn, soybeans, and ornamentals. That enormous diet makes Washington’s agricultural landscape, particularly its apple and pear orchards in the eastern part of the state, highly vulnerable. The bug feeds by piercing plant tissue and sucking out juices, leaving behind deformed spots and rotten blemishes that make produce unsellable. In the eastern United States, it has already caused severe losses in apple yields.
For homeowners, the problem is more personal. Stink bugs are drawn to human-made structures when temperatures drop in fall, and they can enter homes in huge numbers to ride out the winter. They don’t damage your house or reproduce indoors, but finding dozens or hundreds of them clustered in attics, wall voids, and window frames is a common complaint across the state.
When Stink Bugs Are Most Active
Stink bugs follow a predictable seasonal cycle in Washington. Adults overwinter in sheltered spots, entering a dormant state called diapause in late fall. As temperatures warm in spring, they gradually leave their hiding places. Females become reproductively active when daylight stretches to about 12 to 13 hours per day, roughly late March through April in Washington.
Trapping data from eastern Washington shows two distinct peaks of adult activity: one in mid to late May and a second, larger surge in July and August. That summer peak coincides with fruit development, which is when crop damage is most severe. Then, as fall arrives, the cycle restarts. Adults begin seeking winter shelter, and that’s when they press into homes through any gap they can find.
How to Identify Them
Washington is home to several native stink bug species, so confirming you’re looking at the invasive brown marmorated variety matters. Adults are among the larger stink bugs in the state, roughly half an inch to two-thirds of an inch long, mottled brown, and shield-shaped. Two features set them apart from lookalikes:
- White-banded antennae. The antennae have distinct alternating dark and light bands. Native species like the rough stink bug and consperse stink bug have solid-colored antennae.
- Smooth shoulder edges. Looking down at the bug, the front edge of its “shoulders” (the prothorax) is smooth. The rough stink bug has a coarsely toothed edge there, and the consperse stink bug has a finely toothed one.
Brown marmorated stink bugs also have alternating light and dark banding around the edges of the abdomen, though that feature alone isn’t enough to confirm the species. Another common lookalike, stink bugs in the genus Chlorochroa, are also brown but have a smooth white margin along the body and a white dot where the forewings meet at the back.
Are They Harmful to People or Pets?
Stink bugs do not bite, sting, or carry diseases. They aren’t venomous or poisonous. Their only defense is the foul-smelling chemical they release when crushed or threatened, which is why squashing them indoors is a bad idea. In rare cases, those secretions can cause mild skin irritation or minor respiratory symptoms in people with sensitivities, but serious allergic reactions are uncommon.
Pets are similarly safe. If a cat or dog eats a stink bug, the bitter defensive chemicals can cause temporary drooling, vomiting, or diarrhea. These symptoms are short-lived and resolve on their own. The only real concern would be a pet eating a very large number of bugs, which could theoretically cause a digestive blockage, but that’s an unusual scenario.
Keeping Them Out of Your Home
Physical exclusion is the most effective long-term strategy, and the work needs to happen before fall, ideally in late summer, while stink bugs are still outside. The goal is eliminating every gap large enough for a bug to squeeze through. Even a crack of one-sixteenth of an inch is enough for insects to enter.
Start with doors. Install door sweeps or thresholds on all exterior doors, paying special attention to the bottom corners where gaps tend to be widest. Lie on the floor and look for daylight under the door. For garage doors, use a rubber bottom seal (vinyl cracks in cold weather). Sliding glass doors can be sealed by lining the bottom track with half-inch to three-quarter-inch foam weatherstripping.
Next, check windows and siding. Caulk cracks around window frames, door frames, and fascia boards with a good-quality silicone or acrylic latex caulk. Clear-drying caulk is more forgiving of mistakes than pigmented types. Repair any torn or gapped window and door screens.
Utility penetrations are another major entry route. Seal gaps around outdoor faucets, electrical receptacles, gas meters, dryer vents, and cable or phone lines using caulk, expandable foam, steel wool, or copper mesh. Cover attic, roof, and crawl space vents with quarter-inch wire mesh hardware cloth.
Dealing With Stink Bugs Already Inside
Once stink bugs are overwintering in your walls or attic, there’s no great way to flush them all out. Pesticide sprays inside the home are generally ineffective because the bugs are hidden deep in wall voids and other inaccessible spaces. They’ll emerge one or a few at a time on warm days throughout winter and into spring.
A vacuum cleaner is the simplest removal tool. Use it to pick up any bugs you see, then empty the canister or dispose of the bag promptly to avoid the smell building up inside the vacuum. You can also capture individual bugs in a jar or tissue and release or dispose of them outside. Avoid crushing them indoors. The defensive odor is persistent and unpleasant, and the yellowish secretion can stain fabric and painted surfaces.
Garden and Yard Damage
In home gardens, stink bugs target tomatoes, peppers, beans, corn, and a wide range of fruit. Their feeding creates small necrotic patches, sunken spots that turn brown or corky, on whatever they pierce. On fruit like apples or pears, this shows up as dimpled, deformed areas that make the fruit unappetizing even if it’s technically still edible.
Homeowners often notice garden damage before they see the bugs themselves, since the insects are well-camouflaged and tend to feed on the undersides of fruit or deep within plant canopies. Checking plants in the early morning, when stink bugs are less mobile, is the easiest time to spot and hand-remove them. Row covers can protect smaller vegetable plantings, and keeping your garden clear of debris reduces nearby hiding spots.